Process for producing phosphor and plasma display panel unit

ABSTRACT

Fine particles of a phosphor are weighed, mixed, and filled. Provided after this step are at least one step of firing the particles in a reducing atmosphere, and a step of pulverizing, dispersing, rinsing, drying and then treating the particles in an oxygen plasma atmosphere after the last step of treatment in the reducing atmosphere. This method recovers oxygen vacancy in the host crystal of the phosphor.

TECNICAL FIELD

The present invention relates to a plasma display panel device and amethod of fabricating phosphors therefor. Especially, the phosphors canpreferably be used for image display devices represented by a plasmadisplay device, and illuminators represented by a rare-gas dischargelamp and a high-load fluorescent lamp.

BACKGROUND ART

Among color display devices used for image display on a computer ortelevision screen, a plasma display panel device has recently beendrawing attention, as a large and thin color display device having lightweight.

A plasma display device performs additive color mixing of three primarycolors (red, green, and blue) to provide full-color display. For thefull-color display, a plasma display device has phosphor layers foremitting the respective three primary colors, i.e. red, green, and blue.In discharge cells of a plasma display device, discharge of a rare gasgenerates ultraviolet light having a wavelength up to 200 nm. Theultraviolet light excites phosphors of respective colors to generatevisible light of respective colors.

Known as phosphors of the respective colors are (Y, Gd) BO₃:Eu³⁺ andY₂O₃:Eu³⁺ for red emission, (Ba, Sr, Mg)O.aAl₂O₃:Mn²⁺ and Zn₂SiO₄:Mn²⁺for green emission, and BaMgAl₁₀O₁₇:Eu²⁺ for blue emission, for example.

Among these, for a blue phosphor called BAM that contains BaMgAl₁₀O₁₇ asits base material, Eu, i.e. its center of emission, must be activateddivalent, in order to improve emission luminance. Thus, this phosphor isfabricated by firing in a reducing atmosphere (see “Phosphor Handbook”,Phosphor Research Society, Ohmsha, pp.170, for example.) This isbecause, if the phosphor is fired in an oxidizing atmosphere, Eu isactivated trivalent and Eu cannot substitutes for the bivalent Baposition properly in its host crystal. For this reason, Eu cannot be anactive emission center, and this deteriorates emission luminance.Further, Eu does not accomplish its original purpose, and generates redemission peculiar to Eu³⁺.

For a red phosphor, europium-activated yttrium oxysulfide (Y₂O₂S:Eu³⁺),because Eu must be activated trivalent, the phosphor is fabricated byfiring in an oxidizing atmosphere. Meanwhile, for a phosphor in whichits host crystal is made of an oxide, it is considered that oxygen atomsare deprived from the host crystal in firing and thus oxygen vacancy isgenerated in the phosphor. Disclosed as a method of recovering suchoxygen vacancy is firing the materials in an inert gas containing oxygento activate Eu trivalent and provide Y₂O₂S:Eu³⁺ (see Japanese PatentUnexamined Publication No.2000-290649).

However, in comparison with an oxide phosphor fabricated by firing in anoxidizing atmosphere, for an oxide phosphor fabricated by firing in areducing atmosphere, the reducing atmosphere tends to deprive oxygenfrom the host crystal and oxygen vacancy in the host crystal increases.Further, when an oxide phosphor that must be fired in a reducingatmosphere is fired in an oxidizing atmosphere, keeping the number ofvalences inherent in the activator is difficult.

In other words, when a phosphor having much oxygen vacancy in its hostcrystal is subjected to high-energy ultraviolet light (having awavelength of 147 nm) irradiated by a plasma display device and ionimpact caused by discharge, the phosphor is likely to degrade with time.This is because, in the sites having oxygen vacancy, the bond betweenatoms is weak, and application of high-energy ultraviolet light and ionimpact to the sites tends to disturb the crystal structure and make thesites amorphous. The amorphous sites mean deterioration of the hostcrystal. In a plasma display device, such deterioration leads toluminance degradation with time, color shift caused by chromaticitychange, and image burn.

When an oxide phosphor that must be fired in a reducing atmosphere isfired in an oxygen atmosphere for the purpose of recovery of oxygenvacancy, for a BAM phosphor, for example, Eu is activated to Eu³⁺ andthis causes considerable luminance degradation.

The present invention addresses these problems, and aims to provide amethod of fabricating a phosphor, and a plasma display panel using thephosphor. With the fabricating method, even for a phosphor in which itsemission center, Eu or Mn, must be activated bivalent, and its hostcrystal is made of an oxide, its oxygen vacancy can be recovered withoutdeterioration of emission luminance.

DISCLOSURE OF THE INVENTION

The present invention is a plasma display device in which a plurality ofdischarge cells having at least one color is disposed, phosphor layershaving a color corresponding to the respective discharge cells aredisposed, and the phosphor layers are excited by ultraviolet light toemit light. At least one phosphor layer among the phosphor layers ismade of a phosphor that has a composition formula ofBa_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(X) and is treated in an oxygen plasmaatmosphere.

The phosphor of such composition has a high emission luminance.Additionally, the treatment in the oxygen plasma atmosphere can recoveroxygen vacancy in the host crystal without decreasing the emissionluminance, thus providing a plasma display device having inhibitedluminance degradation during actual operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method of fabricating a phosphor inaccordance with an exemplary embodiment of the present invention.

FIG. 2 is a sectional view of a treatment device in a step of treatmentin an oxygen plasma atmosphere in accordance with the exemplaryembodiment of the present invention.

FIG. 3 is a perspective view of an essential part of a plasma displaydevice in accordance with the exemplary embodiment of the presentinvention.

FIG. 4 is a graph showing a luminance degradation factor of the phosphorfor use in the plasma display device in accordance with the exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

An exemplary embodiment of the present invention is detailed hereinafterwith reference to the accompanying drawings.

FIG. 1 is a flowchart showing a method of fabricating a phosphor inaccordance with the exemplary embodiment of the present invention.Synthesis of an aluminate phosphor, Ba_((l.x.y))Sr_(y)MgAl₁₀O₁₇;Eu_(X),is taken as an example.

In step 1, a step of weighing fine particles, generally the followingcarbonates, oxides, and hydrates are used and weighed as the materialsof respective metals. In other words, barium compounds, e.g. bariumcarbonate, barium hydrate, barium oxide, and barium nitrate, are used asbarium materials. Strontium compounds, e.g. strontium carbonate,strontium hydrate, and strontium nitrate, are used as strontiummaterials. Magnesium compounds, e.g. magnesium carbonate, magnesiumhydrate, magnesium oxide, and magnesium nitrate, are used as magnesiummaterials. Aluminum compounds, e.g. aluminum oxide, aluminum hydrate,and aluminum nitrate, are used as aluminum materials. Europiumcompounds, e.g. europium oxide, europium carbonate, europium hydrate,and europium nitrate, are used as europium materials. These materialsare weighed out so as to have a predetermined molar ratio ofconstituting ions. Each material is not limited to carbonate, oxide, orhydrate, and can be any compound.

In step 2, a mixing step, a fluxing agent, i.e. a crystal growthaccelerator, such as aluminum fluoride, barium fluoride, and magnesiumfluoride, is mixed into the weighed materials, as required. In thisembodiment, a ball mill is used as a mixing means, for example, to mixthe materials for one to five hours. The materials can be mixed using aball mill by a wet method. However, instead of the mixing method using aball mill, a co-precipitation method, a method of mixing materials madeof alkoxide of respective metals in a liquid phase, or other methods canbe used.

In step 3, a filling step, such a mixture is filled into aheat-resistant crucible, such as a high-purity alumina crucible.

In step 4, a step of treatment in atmospheric air, the mixed powdersfilled in the crucible is fired in atmospheric air at temperaturesranging from 800 to 1,500° C. for one to 10 hours so that the growth ofthe host crystal is accelerated. Incidentally, because step 4 is foraccelerating the crystal growth, it is not an essential step.

In step 5, a step of treatment in a reducing atmosphere, the mixedpowders filled are fired in a reducing atmosphere, e.g. nitrogenatmosphere, at temperatures at which a desired crystal structure can beformed. The aluminate phosphor of the exemplary embodiment of thepresent invention is fired in the temperature range of 1,100 to 1,500°C., for one to 50 hours.

In step 6, a step of treatment in an oxygen plasma atmosphere, phosphorpowders of predetermined sizes are exposed to an oxygen plasmaatmosphere at temperatures ranging from 400 to 450° C., for one to twohours. Treatment in this atmosphere allows oxygen atoms to enter intothe oxygen vacancy of the host crystal generated during the treatment inthe reducing atmosphere, and thus the oxygen vacancy is recovered.

In step 7, a step of pulverizing, dispersing, rinsing and drying thephosphor, after the mixed powders treated in the oxygen plasmaatmosphere is sufficiently cooled, they are pulverized, dispersed, andrinsed by a wet method for one hour using a bead mill, for example, as adispersing means. Now, the mixed powders can be pulverized and dispersedusing any dispersing device, e.g. a ball mill and jet mill, other thanthe bead mill. Thereafter, the phosphor powders pulverized, dispersed,and rinsed are dehydrated, and sufficiently dried; then sieved out toprovide phosphor powders.

In this embodiment, the step of treatment in a reducing atmosphere andthe following step of treatment in an oxygen plasma atmosphere areperformed once each. However, the step of treatment in a reducingatmosphere to enhance luminance by activating Eu bivalent, and the stepof treatment in an oxygen plasma atmosphere to recover oxygen vacancy inthe host crystal can be repeated a plurality of times. Additionally, oneor more step of treatment in atmospheric air to accelerate the growth ofthe host crystal can be provided before the step of treatment in areducing atmosphere. After each treatment step, the powders can bepulverized, dispersed, and rinsed.

FIG. 2 is a sectional view of a treatment device in a step of treatmentin an oxygen plasma atmosphere in accordance with the exemplaryembodiment of the present invention. The temperature of vacuum chamber41 can be controlled by heater 42. Oxygen gas 43A is supplied from gasentrance 43 and changed to plasma by radio-frequency (RF) plasma device44 having a frequency of 13.56 kHz, a plasma excitation source. Thus,extremely active oxygen gas is provided. After inlet valve 45 is opened,phosphor 40 having oxygen vacancy is fed into the vacuum chamber, andcontinuously dropped by the small amount. Thus, when phosphor 40 havingoxygen vacancy is exposed to active oxygen gas 43A, the phosphor ischanged to phosphor 49 having oxygen vacancy recovered and dropped.

For complete oxygen vacancy recovery, transfer pipe valve 46 is openedto allow phosphor 40. having oxygen vacancy to go upward throughtransfer pipe 48 and drop into vacuum chamber 41 again. This operationis repeated until the oxygen vacancy is completely recovered. Afterphosphor 40 having oxygen vacancy undergoes a predetermined oxygenvacancy recovery treatment, it is taken out by relieving vacuum andopening exhaust valve 47.

Next, various kinds of aluminate phosphors,Ba_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(X), are treated at least in a reducingatmosphere and then treated in an oxygen plasma atmosphere. Thecharacteristics of respective aluminate phosphors are describedaccording to the examples.

EXAMPLE 1

Powders of sufficiently dry barium carbonate [BaCO₃], magnesiumcarbonate [MgCO₃],. europium oxide [Eu₂O₃], and aluminum oxide [Al₂O₃]are prepared as the materials. These materials are weighed out so as tohave a molar ratio of constituting ions ofBa:Mg:Eu:Al=0.99:1.00:0.01:10.00. Next, after aluminum fluoride is addedto the weighed materials, as a crystal growth accelerator, the mixtureis mixed for three hours using a ball mill.

Next, the mixture is filled into a high-purity alumina crucible andfired in atmospheric air at a temperature of 1,200° C. for one hour.Then, the mixed powders fired are fired again in a reducing atmospherecontaining 20% of nitrogen gas and 80% of hydrogen gas,. at 1,200° C.for 10 hours. Sequentially, after the fired powders are pulverized,dispersed, rinsed, dried, and classified, they are exposed to oxygenplasma several times (for one hour) using the device for treatment in anoxygen plasma atmosphere of FIG. 2. In the treatment device, thetemperature in the chamber is 400° C.

Then, the powders subjected to these treatments are rinsed. The rinsedmixed power phosphor is dehydrated, sufficiently dried, and then sievedout to provide phosphor powder having a general formula of Ba _(0.99)MgAl₁₀O₁₇:Eu_(0.01.)

Next, the fabricated phosphor powder is irradiated with vacuumultraviolet light having a peak wavelength of 146 nm obtained by avacuum ultraviolet excimer laser irradiation equipment (146-nm lightirradiation equipment manufactured by Ushio Inc.), and the luminancewith respect to the irradiation time is measured using a luminance meter(LS-110 manufactured by Konika Minolta Japan). In this invention, as thecharacteristic value of luminance, a relative luminance value definedhereinafter is set to a performance index. The relative luminance valueis obtained by multiplying the relative initial luminance of eachphosphor by a luminance sustaining factor. Now, the relative initialluminance is defined as follows. When the initial luminance of aconventional phosphor is set to 100, the rate of the initial luminanceof each example is indicated by the relative initial luminance. Theluminance sustaining factor is a percentage obtained by dividing theluminance of the material of each example after 5,000 hours by itsinitial luminance. In other words, the relative luminance value is forcomparing the luminance of phosphors after a curtain period between theconventional phosphor and the phosphor of the example. The ratios ofconstituting materials, treatment conditions, and relative luminancevalues are shown in Table 1.

EXAMPLES 2 and 3

Example 2 is made of the same materials as Example 1; however, it has amolar ratio of constituting ions of Ba:Mg:Eu:Al=0.9:1.0:0.1:10.0.Example 3 is also made of the same materials as Example 1; however, ithas a molar ratio of constituting ions of Ba:Mg:Eu:Al=0.8:1.0:0.2:10.0.The difference between Examples 2 and 3, and Example 1 is as follows.For Example 2, the mixture is fired in atmospheric air at 1,400° C. forone hour, and in a reducing atmosphere having a partial pressure ratioof N₂:H₂ =95:5 at 1,100° C. for 10 hours. For Example 3, the mixture isfired in atmospheric air at 800° C. for one hour, and in a reducingatmosphere having a partial pressure ratio of 100% of N₂ at 1,200° C.for 10 hours. Then, phosphor powders fabricated under these conditionsare evaluated using the relative luminance values like Example 1. Table1 shows treatment conditions, relative luminance values, and otherresults.

EXAMPLES 4 through 9

For all these examples, powder of strontium carbonate [SrCO₃] is addedto the materials of Example 1. However, Example 4 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.89:0.10:1.00:0.01:10.00. Example 5has a molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.8:0.1:1.0:0.1:10.0. Example 6 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.7:0.1:1.0:0.2:10.0. Example 7 hasa molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.69:0.30:1.00:0.01:10.00. Example 8 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.6:0.3:1.0:0.1:10.0. Example 9 hasa molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.5:0.3:1.0:0.2:10.0. The difference between Examples 4through 9 and Example 1 is as follows. Example 4 is not fired inatmospheric air, and fired in a reducing atmosphere having a partialpressure ratio of 100% of H₂ at 1,100° C. for 10 hours. Example 5 isfired in atmospheric air at 1,300° C. for one hour, and in a reducingatmosphere having a partial pressure ratio of N₂:H₂ =99:1 at 1,200° C.for 10 hours. Example 6 is fired in atmospheric air at 1,400° C. for onehour, and in a reducing atmosphere having a partial pressure ratio ofN₂:H₂ =90:10 at 1,400° C. for 10 hours. Example 7 is fired inatmospheric air at 1,300° C. for one hour, and in a reducing atmospherehaving a partial pressure ratio of N₂:H₂ =98:2 at 1,300° C. for 10hours. Example 8 is fired in atmospheric air at 1,000° C. for one hour,and in a reducing atmosphere having a partial pressure ratio of N₂:H₂=90:10 at 1,300° C. for 10 hours. Example 9 is fired in atmospheric airat 1,200° C. for one hour, and in a reducing atmosphere having a partialpressure ratio of N₂:H₂ =50:50 at 1,300° C. for 10 hours. Then, phosphorpowders fabricated under these conditions are evaluated using therelative luminance values like Example 1. Table 1 shows treatmentconditions, relative luminance values, and other results. TABLE 1Reducing Molar ratio of atmosphere Oxygen constituting AtmosphericTemperature plasma Relative ions air H₂ atmosphere luminance Ba Sr EuGeneral formula Temperature concentration Temperature value Example 10.99 0 0.01 Ba_(0.99)MgA₁₁₀O₁₇:Eu_(0.01) 1200° C. 1200° C. 400° C. 7580% Example 2 0.9 0 0.1 Ba_(0.9)MgAl₁₀O₁₇:Eu_(0.1) 1400 1100 95 5Example 3 0.8 0 0.2 Ba_(0.8)MgAl₁₀O₁₇:Eu_(0.2)  800 1200 91 0 Example 40.89 0.1 0.01 Ba_(0.89)Sr_(0.1)MgAl₁₀O₁₇:Eu_(0.01) — 1100 74 100 Example5 0.8 0.1 0.1 Ba_(0.8)Sr_(0.1)MgAl₁₀O₁₇:Eu_(0.1) 1300 1200 90 1 Example6 0.7 0.1 0.2 Ba_(0.7)Sr_(0.1)MgAl₁₀O₁₇:Eu_(0.2) 1400 1400 94 10 Example7 0.69 0.3 0.01 Ba_(0.69)Sr_(0.3)MgAl₁₀O₁₇:Eu_(0.01) 1300 1300 75 2Example 8 0.6 0.3 0.1 Ba_(0.6)Sr_(0.3)MgAl₁₀O₁₇:Eu_(0.1) 1000 1300 96 10Example 9 0.5 0.3 0.2 Ba_(0.5)Sr_(0.3)MgAl₁₀O₁₇:Eu_(0.2) 1200 1300 75 50Comparative 0.8 0.1 0.1 Ba_(0.8)Sr_(0.1)MgAl₁₀O₁₇:Eu_(0.1) 1300 1200 —69 Example 1

COMPARATIVE EXAMPLE

As a comparative example, a phosphor having the same molar ratio of theconstituting ions as Example 5 is fabricated by the conventionalfabricating method (conventional phosphor). The difference from Example5 is that comparative example is not treated in an oxygen plasmaatmosphere for oxygen vacancy recovery. The luminance sustaining factorof this sample is 69%, and thus the relative luminance value is 69.

As obvious from Table 1, the average relative luminance value ofaluminate phosphors of Ba_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(X) is larger thanthe relative luminance value of the comparative example, theconventional phosphor, by 16, in the range of 0.01≦x≦0.20 and 0≦y≦0.30,and the emission luminance has increased. When the amount of Ba, Sr, andEu, i.e. x and y, in the aluminate phosphors ofBa_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(X) are within the above range,remarkable effects are obtained. However, for the amount of Mg and Al,when they are within the composition range of approximately ±5% of theabove molar quantities (Mg=1, and Al=10), the effect of improvingemission efficiency has not changed.

In Examples 1 through 9, conditions for firing in reducing atmospheresand preceding conditions for firing in atmospheric air for fabricatingthe samples are varied. However, it is considered that not the influenceof these different conditions on the relative luminance values, but theexistence of treatment in an oxygen plasma atmosphere leads to thedifference in the relative luminance values. This is because adifference in the relative luminance value of 20 is observed especiallybetween Example 5 and the comparative example, in which the molar ratioof the constituting ions is identical but the existence of treatment inoxygen plasma atmosphere for oxygen vacancy recovery is different.Further, the effect of treatment in an oxygen plasma atmosphere can beinferred from the following reasons.

Firstly, Eu is often used as an activator that can be bivalent andtrivalent. In the example of BAM, a blue phosphor, it is necessary thatbivalent Ba substitutes for bivalent Eu while the host crystal ofBa_((l.x))MgAl₁₀O₁₇ is grown from its materials, to produce a stableemission center Eu²⁺. For this purpose, as a conventional basic firingmethod, the materials are fired in an appropriate reducing atmosphere athigh temperatures ranging from 1,000 to 1,500° C., for at least fourhours.

Secondly, as to the recovery of the oxygen vacancy of the host crystalgenerated in the reducing atmosphere, the effect of recovering oxygenvacancy has been recognized when the phosphor is continuously treated inan oxygen plasma atmosphere at temperatures ranging from 400 to 450° C.

Incidentally, Sr need not be contained in the composition of thephosphor. However, if Sr is contained, Sr²⁺ having a smaller iondiameter substitutes for a part of Ba²⁺, and the lattice constant of thecrystal structure is slightly reduced. Thus, the emission color of theblue phosphor can be made more desirable color.

Next, FIG. 3 is a perspective view of an essential part of a plasmadisplay device in accordance with the exemplary embodiment of thepresent invention. In front panel 10, display electrodes 15, each madeof scan electrode 12 a and sustain electrode 12 b, and dielectric layer13 covering display electrodes 15 are formed on transparent andinsulating front substrate 11. Further on this dielectric layer 13,protective layer 14 is formed.

A predetermined number of display electrodes 15 are formed at a constantpitch on front substrate 11. Dielectric layer 13 is generally formed byprinting and firing low-melting glass because the dielectric layer isformed after formation of display electrodes 15 to securely cover thesedisplay electrodes 15. As the materials of the glass paste, alow-melting glass paste having the composition of so-called(PbO—SiO₂—B₂O₃—ZnO—BaO) glass, containing lead monoxide [PbO], siliconoxide [SiO₂], boron oxide [B₂O₃], zinc oxide [ZnO], and barium oxide[BaO], can be used. Using this glass paste and repeating screen-printingand firing, for example, can easily provide dielectric layer 13 having apredetermined thickness. The thickness may be set according to thethickness of display electrodes 15 and target electrostatic capacity orother factors. In this embodiment of the present invention, thethickness of dielectric layer 13 is approximately 40 μm. Additionally, aglass paste containing at least one of lead monoxide [PbO], bismuthoxide [Bi₂O₃], and phosphorus oxide [P0₄] as a major constituent can beused.

Protective layer 14 is provided so that plasma discharge does notsputter dielectric layer 13. Thus, the protective layer is required tobe a highly sputtering-resistant material. For this reason, magnesiumoxide [MgO] is often used.

On the other hand, on rear substrate 16 that is transparent andinsulating like the front substrate, data electrodes 17 for writingimage data are formed in the direction perpendicular to displayelectrodes 15 on front panel 10. After insulating layer 18 is formed onrear substrate 16 to cover these data electrodes 17, barrier rib 19 isformed in parallel with and substantially at the center of each dataelectrode 17. The areas sandwiched between barrier ribs 19, phosphorlayers 20 are formed to constitute rear panel 50. These phosphor layers20 are formed adjacent to phosphors emitting red (R), green (G), or blue(G) light. These phosphor layers constitute pixels.

Formed as data electrodes 17 are films having laminated structures, suchas a single-layer film made of silver, aluminum, or cupper having lowelectric resistance, a two-layer film made of chromium and cupper, and athree-layer film made of chromium, cupper, and chromium, using thin-filmforming techniques, such as printing and firing, or sputtering.Insulating layer 18 can be formed by the same materials and film-formingmethods as dielectric layer 13. Additionally, a glass paste containingat least one of lead monoxide [PbO], bismuth oxide [Bi₂O₃], andphosphorus oxide [P0₄] as a major constituent can be used. The phosphorsfabricated by the above methods and emitting R, G, or B light areapplied to the areas sandwiched between barrier ribs 19 by an inkjetmethod, for example, to form phosphor layers 20.

When front panel 10 and rear panel 50 are faced with each other,discharge space 30 surrounded by barrier ribs 19, protective layer 14 onfront substrate 11, and phosphor layers 20 on rear substrate 16 isformed. Then, when this discharge space 30 is filled with a mixed gas ofNe and Xe at a pressure of approximately 66.5 kPa, and alternatingvoltages ranging from several dozens to several hundred kilohertz areapplied across each scan electrode 12 a and corresponding sustainelectrode 12 b for discharge, phosphor layers 20 can be excited byultraviolet light generated when excited Xe atoms return to their groundstate. This excitation causes phosphor layers 20 to emit R, G, or Blight according to the materials applied thereto. For this reason, whenthe pixels at which data electrodes 17 emit light and colors of thelight are selected, necessary colors can be emitted at predeterminedpixel sections for color image display.

FIG. 4 is a graph showing luminance degradation factors of the phosphorsfor use in the plasma display device. Pulse voltages having an amplitudeof 180V and a frequency of 15 kHz are. applied across display electrodes15. The variations of emission luminance with time are examined for thephosphor of Example 5 fabricated in accordance with the exemplaryembodiment of the present invention and the phosphor of the comparativeexample fabricated by the conventional method. The initial emissionluminance is set to 100% and the emission luminance after each lightingperiod is divided by the initial emission luminance to provide aluminance degradation factor. For the phosphor fabricated by theconventional method, the luminance degradation factor after 5,000 hoursdecreases to 72%. In contrast, for the phosphor fabricated in accordancewith this. exemplary embodiment of the present invention, an emissionluminance of 85% is maintained. Even only in terms of the luminancedegradation factor, an improvement of 13% has obtained, and luminancedegradation has been inhibited. This is because the phosphor fabricatedin accordance with this exemplary embodiment is treated in an oxygenplasma atmosphere after being fired in a reducing atmosphere, and thushas less oxygen vacancy and a smaller part of anamorphous structure inits crystal structure. As a result, even with irradiation of ultravioletlight or ion impact applied thereto, degradation of the crystalstructure and thus luminance degradation are smaller.

In the description of this exemplary embodiment of the presentinvention, Eu²⁺ is used as an activator in BAM phosphors. However, alsofor other phosphors using Eu²⁺ as an activator, such as CaMgSi₂O₆:Eu,and a green phosphor (Ba, Sr, Mg)O.aAl₂O₃:Mn in which Mn²⁺ is used as anactivator and its host crystal is made of an oxide, treatment in anoxygen plasma atmosphere has effects of increasing emission luminanceand inhibiting luminance degradation.

The present invention provides a method of fabricating a phosphorcapable of recovering its oxygen vacancy without decreasing its emissionluminance, even in the case of a phosphor in which its emission center,Eu or Mn, must be activated bivalent and its host crystal is made of anoxide. Further, this fabricating method can provide a plasma displaydevice having higher emission luminance and lower luminance degradation.

Industrial Applicability

The present invention can recover oxygen vacancy of a phosphor withoutdecreasing its emission luminance, even in the case of a phosphor inwhich its emission center, Eu or Mn, must be activated bivalent and itshost crystal is made of an oxide. The present invention is useful toimprove the performance of image display devices represented by a plasmadisplay device and illuminators represented by a rare-gas discharge lampand a high-load fluorescent lamp.

1. A plasma display device in which a plurality of discharge cellshaving at least one color is disposed, phosphor layers having a colorcorresponding to the respective discharge cells are disposed, and thephosphor layers are excited by ultraviolet light to emit light, whereinat least one phosphor layer among the phosphor layers is made of aphosphor that has a composition formula ofBa_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(x)and is treated in an oxygen plasmaatmosphere.
 2. The plasma display device of claim 1, wherein, in thecomposition formula of Ba_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(x), 0.01≦x≦0.20and 0≦y≦0.30.
 3. A method of fabricating a phosphor in which at leastone of Eu and Mn is added as an activator thereof and a multiple oxidecontaining at least one of elements Ba, Ca, Sr, and Mg is a host crystalthereof, the method comprising: firing mixed materials of the phosphorin a reducing atmosphere at least once; and treating the phosphor in anoxygen plasma atmosphere after the step of treatment in the reducingatmosphere.
 4. The method of fabricating a phosphor of claim 3, wherein,a composition formula of the phosphor isBa_((l.x.y))Sr_(y)MgAl₁₀O₁₇:Eu_(x), where 0.01≦x≦0.20 and 0≦y≦0.30.